There exists a requirement for inspection of cargo for the detection of illicit materials and devices. Currently, a popular way of performing such inspection is through the use of X-ray screening equipment.
In this apparatus, a high energy X-ray source (typically a 4 MV to 9 MV X-ray linear accelerator) is collimated to a fan beam which irradiates through the cargo item under inspection through to a set of X-ray detectors in a substantially linear configuration.
To form a two-dimensional image from the set of one-dimensional projection data, it is necessary to scan the cargo item through the X-ray beam. This can be achieved by placing the cargo item on a moving floor which moves the cargo item through the X-ray beam with controlled velocity. Alternatively, the X-ray system can be placed on rails and, with the cargo item stationary, the X-ray system can be scanned along the rails to form the image. Alternatively, the X-ray system can be mounted on a vehicle which can be driven past the stationary cargo item to form the image. Alternatively, the cargo item can be dragged through a stationary X-ray beam using a tow truck.